In the fabrication of a semiconductor device, such as a solid state transistor, several thin film processes are involved. In brief, and for example, the silicon wafer is first wet cleaned and then a film of silicon oxide is formed by heating the wafer in an oxygen environment at an elevated temperature. After the silicon oxide film is formed, a silicon nitride film is deposited on the oxide film. This deposition of the silicon nitride film is achieved using ammonia and silane in a low pressure chemical vapor deposition system. A field oxide is then deposited after several serial steps of dry etch removal of deposited resist, wet clean, oxidation and final planarization in various equipment sets. The circuit pattern begins to shape up by several lithographic processes of the transistor design that is intended to be used. The N-well and the P-well that form the source and drain of the transistor are then created by separate ion implant, resist ashing, and wet clean steps.
A rigorous wafer wet pre-clean then typically follows using various concentrations of inorganic acids such as hydrofluoric acid. The wafer is then oxidized at elevated temperature ranging from 600xc2x0 C. to 1050xc2x0 C. in ambients such as oxygen, oxygen with dichlorosilane and water vapor, or oxygen and hydrogen. This oxide, called the transistor gate oxide, is then typically annealed at high temperature, near 1000xc2x0 C., in nitrogen ambient with ammonia or nitrous oxide. This last annealing step forms a layer of silicon nitride which usually incorporates a certain amount of nitrogen within the gate oxide. Silicon nitride is a good conductor as well as an excellent diffusion barrier. When a polysilicon layer is added, which typically contains Boron or Phosphorous, the Boron or Phosphorous atoms can migrate into the gate oxide. The silicon nitride layer, however, acts as a barrier for Boron or Phosphorous migration into the gate. However, as gates get thinner on the order of 20 Angstroms, nitrogen atoms present in the oxide layer affect the performance of the gate. Therefore, the nitrogen migration has become an impediment to increasing the speed of many devices. As the device fabrication geometries have gotten smaller, and nearing the 0.13 micron line width, the nitrogen incorporation within the gate oxide as a diffusion barrier have limited further gains in the speed of these devices.
Consequently, there is a need for a method in which the Phosphorous or Boron atoms that are located in the polysilicon layer for migrating into the gate oxide while able to minimize the gate oxide thickness.
According to the present invention, a method of fabricating a semiconductor device induces incorporating nitrogen atoms at the oxide film-polysilicon layer interface of the device. The present invention provides a process that incorporates nitrogen atoms in such a way that most, if not all, the atoms reside above the oxide film surface and not within it. This offers maximum Boron atom diffusion prevention from the polysilicon layer, which allows the oxide film to function in a most desirable electrical fashion at very low thicknesses approaching 8 to 15 Angstroms, which increases the speed of the device.
In one form of the invention, a semiconductor device is fabricated by forming an oxide film in a semiconductor substrate followed by adding nitrogen atoms on top of the exposed surface of the semiconductor substrate to form a diffusion barrier wherein the nitrogen atoms do not penetrate the oxide film.
In one aspect, the nitrogen atoms are added by exposing the substrate to a plasma containing nitrogen gas. For example, the substrate may be exposed to the plasma in a temperature in a range of 25xc2x0 C. to 800xc2x0 C. or in a temperature of about 25xc2x0 C. In a further aspect, the substrate is exposed to a nitrogen plasma in a pressure in a range of 10 mTorr to 1000 mTorr or, more preferably, in a pressure of about 150 mTorr.
In another aspect, the substrate is also exposed to helium gas. Preferably, the substrate is exposed to a plasma containing nitrogen gas and helium gas.
In yet another aspect, the substrate is exposed to a plasma containing nitrogen gas in the presence of silane gas wherein the nitrogen and silane form a silicon nitride film on top of the oxide film. For example, the substrate may be exposed to a plasma containing nitrogen gas in the presence of silane gas in a pressure in a range of about 50 mTorr to 750 mTorr or in a pressure of about 250 mTorr.
According to another form of the invention, a semiconductor device is fabricated by forming an oxide film in a substrate with the film having an exposed surface and an interface surface with the substrate. The exposed surface is exposed to silane gas to form silane molecules on the exposed surface. Nitrogen atoms are added on top of the exposed surface of the oxide film wherein the nitrogen atoms react with the silane molecules to form a diffusion barrier.
In one aspect, the nitrogen atoms are added by exposing the substrate to a plasma containing nitrogen gas. For example, the substrate may be exposed to the plasma containing nitrogen gas in a temperature in a range of 25xc2x0 C. to 800xc2x0 C. or in a temperature of about 25xc2x0 C.
In yet another form of the invention, a semiconductor device is fabricated in a processing chamber of a processing apparatus by forming an oxide film in a semiconductor substrate. A plasma containing a nitrogen gas is injected into the processing chamber in the presence of silane gas to form a diffusion barrier on top of the oxide film.
In one aspect, the plasma is injected into the processing chamber under a pressure in a range of about 50 mTorr to 750 mTorr or, more preferably, of about 250 mTorr.
In another aspect, silane gas is injected into the processing chamber with a gas flow in a range of about 5 to 50 cm3/min. Preferably, silane gas is injected into the processing chamber with a gas flow of about 25 cm3/min.
According to another aspect, the plasma is generated with a plasma generator with a radio frequency of in a range of about 5 to 50 MHz, and, more preferably, with a radio frequency of about 13.56 MHz. Furthermore, the power input of the plasma generator is in a range about 50 to 1000 Watts, and, more preferably, about 400 Watts.
According to another form of the invention, a semiconductor device is fabricated by adding nitrogen atoms on to the surface of a semiconductor substrate. Thereafter, an oxide film is formed in the substrate over the nitrogen atoms, wherein the nitrogen atoms are incorporated into the oxide film to form a diffusion barrier.
In another form of the invention, a semiconductor device includes a semiconductor substrate, an oxide film formed in the substrate, and a diffusion barrier formed on top of the exposed surface of the oxide film wherein the molecules forming the diffusion barrier do not penetrate the oxide film.
In one aspect, the diffusion barrier includes nitrogen atoms.
In other aspects, the oxide film has a thickness in a range of 10 to 50 Angstroms.
According to another aspect, the oxide layer forms a gate oxide film of a transistor.
In yet other aspects, the diffusion barrier includes nitrogen and silane atoms. Furthermore, the diffusion barrier has a thickness in a range of 5 to 30 Angstroms, and, more preferably, in a range of 15 to 20 Angstroms.
According to yet another form of the invention, a semiconductor device includes a semiconductor substrate, a film formed in the substrate, which comprises a high dielectric material, and a diffusion barrier formed on top of the exposed surface of the film wherein the molecules forming the diffusion barrier do not penetrate the film.
For example, the semiconductor substrate preferably comprises a silicon wafer, with the film comprising at least one material from a group including zirconium oxide and hafnium oxide.
In addition, the diffusion barrier includes nitrogen atoms, and may include both nitrogen and silane atoms.
In further aspects, the diffusion barrier has a thickness in a range of 5 to 30 Angstroms, and, more preferably, in a range of 15 to 20 Angstroms.